fix(command): stop darwin EPERM on zombie-only process groups

[skevetter]

Symptom

macOS unit job fails in TestTerminateUnidentifiedProcessGroup (run 38513437175, job 115686904199):

process_test.go:286: terminateProcessRef: send SIGKILL to process target -37073: operation not permitted

Ubuntu passes.

Root cause

On darwin, kill(-pgid, sig) returns EPERM for a group whose only member is a zombie. The darwin identity matcher counted an exited, unreaped leader as a live member, so the kill path signaled the group and surfaced EPERM. Confirmed on macOS 25.6 arm64: zombie leader reports P_stat=5, Getsid returns ESRCH, and kill(-pgid, 0|TERM|KILL) returns EPERM. The exact CI interleaving is inferred; the probe did not reproduce the timing.

Changes

• process_identity_darwin.go: zombies are never group members; a zombie leader is matched by start time only (no session lookup is possible); add processIsLive and processGroupHasLivingMembers.
• process_identity_linux.go / process_identity_unix.go: same helpers; unsupported platforms fail closed.
• process_supported.go: EPERM from a negative-PGID signal is suppressed only when the saved identity matches no live member (confirmGroupEPERM). Leader liveness is checked before reading identity. processGroupExists (kill(-pgid, 0)) is replaced by a living-member scan.
• Tests: readiness-file fixture for the SIGTERM-ignoring group, darwin zombie tests with a real unreaped zombie, stale-identity test, and EPERM classifier table.

Safety

• Saved identity format and ProcessRef are unchanged.
• No PGID-only signaling; identity stays authoritative, so reused PIDs are not signaled.
• EPERM is not added to isProcessGone. Live, unverifiable, or identity-less cases keep the error.
• Linux semantics and Windows job behavior are unchanged. No workflow changes, retries, skips, sleeps, or timeouts.

Verification (native macOS arm64, go1.26.8)

• go test -race -short -count=100 -run '^TestTerminateUnidentifiedProcessGroup$' ./pkg/command: pass
• -count=20 for TestKillTree|TestTerminate|TestCleanupExited|TestProcessTreeIdentity|TestKillWorkerTree|TestConfirmGroupEPERM|TestDarwin: pass
• go test -race -count=1 ./pkg/command: pass
• go vet on darwin, linux, windows; GOOS=linux go test -c: pass
• golangci-lint ./pkg/command/...: only 2 pre-existing gosec findings (command.go:54, credential_supported.go:32)

Not run locally: Linux test execution (CI covers it).

Rollback

Revert the three commits; no data or format migration.

Review follow-up (Greptile threads, commits c326b73, b022205, dc442b6)

• Linux /proc scan (r4273929331): unreadable non-leader entries are skipped and group absence is confirmed with one kill(-pgid, 0) probe, reusing linuxCanSkipProcessStatError and linuxProcessGroupMatchResult. Unreadable leader, failed listing, or a possibly-live group still fails closed. Tests: TestLinuxLivingGroupMembers, TestProcessGroupHasLivingMembersRejectsNonpositiveGroup.
• Already-gone grace wait (r4273929340): sendProcessSignal returns signalSent or targetGone; signalProcessTree returns right away on targetGone. EPERM rules are unchanged. Tests: TestClassifySignalResult, TestSignalProcessTreeReturnsImmediatelyWhenTargetAlreadyGone.
• Zombie leader with live child (r4273929348): TestDarwinZombieLeaderWithLiveChildKeepsGroupMatched (stdin-gated leader, unreaped, asserts group matched and child terminated) and TestDarwinZombieLeaderWithLiveChildRejectsStaleIdentity.
• Zombie-only test no longer pins the exact EPERM errno; the EPERM branch is covered deterministically by the classifier table.

Locally executed: native macOS arm64 -race -short -count=100 of the Darwin, kill-worker, EPERM and classifier tests, and go test -race -count=1 ./pkg/command; Linux arm64 test binary in a --init container at -count=20; golangci-lint for linux, darwin and windows shows no findings in changed files (2 pre-existing gosec findings remain). CI results for the new head are pending.

Not changed: pre-existing positive-PID first-SIGTERM-before-identity-check ordering in killSingleProcessWithIdentity; it needs a separate scoped follow-up.

Summary by CodeRabbit

• Bug Fixes
  • Improved process cleanup across supported Unix platforms when a process or process group has exited, including cases where zombie processes remain.
  • Prevented cleanup from signaling a process when its identity is stale or the target is already gone.
  • Improved handling of signal and process-status errors, while preserving errors when a target may still be running.
  • Process groups with no living members are now treated as exited, even if zombie processes remain.

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: 083f47b0-7393-4fbf-bf85-7d25ba2884d6

📥 Commits

Reviewing files that changed from the base of the PR and between c326b73 and 1f43a24.

📒 Files selected for processing: 1

• pkg/command/process_test.go

🚧 Files skipped from review as they are similar to previous changes: 1

• pkg/command/process_test.go

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📝 Walkthrough

Process-group cleanup now checks for living members and classifies signal results. Darwin matching excludes zombies, Linux adds /proc-based liveness checks, and other Unix platforms report these checks as unsupported.

Changes: Process group termination

Layer / File(s)	Summary
Process identity and liveness checks pkg/command/process_identity_*	Darwin group matching excludes zombies and validates the leader’s start-time identity. Darwin and Linux add process and group liveness checks. Other Unix platforms return unsupported errors. Platform tests cover zombie groups and process-stat outcomes.
Termination and signal-result handling pkg/command/process_supported.go, pkg/command/process_test.go	Group cleanup checks for living members. Worker-tree termination checks leader liveness and classifies signal results, including ESRCH and group EPERM. Tests cover stale identities, exited targets, and signal-result cases.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant killWorkerTreeWithIdentity
  participant signalProcessTree
  participant syscall.Kill
  participant classifySignalResult
  participant confirmGroupEPERM
  killWorkerTreeWithIdentity->>signalProcessTree: request SIGTERM
  signalProcessTree->>syscall.Kill: send signal to process group
  syscall.Kill-->>classifySignalResult: return signal result
  classifySignalResult->>confirmGroupEPERM: verify identity after group EPERM
  confirmGroupEPERM-->>classifySignalResult: report matching processes or no match
  classifySignalResult-->>signalProcessTree: return sent, gone, or error outcome

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Merge Risk: ⚪ Minimal · up to 1f43a

No identified issue currently blocks merging. Complete the pending CI checks before merge.

Security architecture risk: 🔵 Low · up to c326b

The change preserves saved-identity checks and continues reporting permission failures when matching processes remain or verification fails. No introduced security weakness was established. Remaining risk is concentrated in platform-specific process timing and non-atomic process observations.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The directly affected sensitive outcome is signaling a worker PID or process group under the caller's existing OS signal permissions. The inspected changes alter target verification and error interpretation, not the syscall's credential authority. Tenant, service, and deployment-wide exposure cannot be established from the available dependency coverage.

Trust Boundaries and Controls

• observed — PGID-only liveness is not signaling authority. Identityless exited-group cleanup never signals and returns an error if living members remain or the scan fails. Identity-bearing group termination continues to require the saved-identity matcher.
• observed — Darwin checks a present leader's saved start-time components before excluding zombies, and still requires matching group and session identity for live members. A stale zombie-leader identity is tested to leave its live child running.

Resilience and Maintainability Implications

• observed — Unsupported liveness checks return errors rather than inventing completion. Linux retains unreadable non-leader stat errors when no living member is found unless a separate group probe confirms ESRCH, preventing permission-limited observation from silently establishing absence.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 1.85% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 54 functions across 7 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the primary change: preventing Darwin EPERM errors for zombie-only process groups.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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[skevetter]

@greptileai review

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; all three previous findings are addressed.

Summary

The PR stops macOS cleanup from treating zombie-only process groups as live.

• Darwin group matching skips zombies but still checks the leader’s identity.
• Cleanup checks process groups for living members before calling them active.
• Group signals treat EPERM as done only when saved identity finds no match.

All three previous findings are addressed. No new actionable issues were found.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Send signal] --> B{Signal result}
  B -->|Success| C[Check saved identity before final kill]
  B -->|ESRCH| D[Return success]
  B -->|Group EPERM| E{Saved identity matches a live member?}
  E -->|No| D
  E -->|Yes or cannot check| F[Return error]
  B -->|Other error| F

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_{Reviews (2) · Last reviewed commit: "test(command): cover darwin zombie leade..." · Reviewed by Greptile}

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @pkg/command/process_test.go:
- Around line 506-517: Update
TestSignalProcessTreeReturnsImmediatelyWhenTargetAlreadyGone to use a PID
guaranteed not to identify a live process instead of running and reaping a
process before using its PID; preserve the graceful signal call and
immediate-return assertion.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: Organization UI
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• Plan: Advanced
• Run ID: 345e5015-2ac1-48b8-85e5-52e989d31a91

📥 Commits

Reviewing files that changed from the base of the PR and between 2f3756f and c326b73.

📒 Files selected for processing: 7

• pkg/command/process_identity_darwin.go
• pkg/command/process_identity_darwin_test.go
• pkg/command/process_identity_linux.go
• pkg/command/process_identity_linux_test.go
• pkg/command/process_identity_unix.go
• pkg/command/process_supported.go
• pkg/command/process_test.go

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